In hunting or marine sports area, a pair of binoculars in which a reticle that is a plane glass on which a scale is deposited is fitted on an imaging plane of an objective lens is used.
Such a pair of binoculars is used in the following manner. At first, an object to be observed is captured in a field of view, and the scale is superimposed on the object.
Then, diopter adjustment of right and left optical systems is carried out, and the object to be observed is focused.
Then, the scale is read out to detect a dimension of the object (in the case where a distance to the object has been known), or a distance to the object (in the case where the dimension of the object has been known).
The work to fix the reticle on the imaging plane of the objective lens is carried out after adjusting the position of the reticle on the optical axis in order to focus not only on the object but also on the scale of the reticle upon focusing on a distant object. Accordingly, when the object is located at a distant position, it is relatively easy for an observer to focus on both of the object and the scale of the reticle superimposed in the field of the observer (see Nikon binoculars combined brochure, published on Nov. 16, 2006).
However, when the object to be observed is located at a near distance, since accommodation varies greatly between individuals, it sometimes happens that the observer cannot focus on the object and the scale of the reticle in the field of view at the same time, so that the dimension of the object or the distance from the object cannot be measured.
The present invention is made in view of the above-described problems, and has an object to provide a pair of binoculars capable of measuring a dimension of an object or a distance to the object by using the scale in the field even if the object is located close to the observer.